As a recording system for performing gradation recording using an inkjet head, a multi-drop system is known. In the multi-drop system, ink droplets are ejected from the inkjet head to a predetermined position plural times to print a dot having predetermined density on a medium such as a recording sheet. For example, if a black dot having eight gradations is formed, seven black ink droplets are ejected from the inkjet head. Ink droplets are ejected in a number corresponding to a gradation level, for example, six ink droplets are ejected in the case of seven gradations and five ink droplets are ejected in the case of six gradations. If a white dot is formed, no ink droplet is ejected from the inkjet head (one gradation). If a gray dot is formed, one to three ink droplets are ejected from the inkjet heads to the same position. In this way, the number of times ink droplets are ejected from the inkjet head is selectively changed to print a high-quality image.
In the inkjet head of the multi-drop system, depending on a type of ink and setting conditions, a satellite drop occurs after plural ink droplets (hereinafter referred to as main drops) are ejected. The satellite drop is a small ink droplet formed when the main drops are ejected from a nozzle of the inkjet head.
The plural main drops and the satellite drop are dripped to a predetermined position, whereby dots are formed on the medium. It is likely that a small dot is formed by the satellite drop (hereinafter referred to as satellite dot) near a dot formed by the plural main drops (hereinafter referred to as main dot).